The use of stents and materials for stents has gained popularity with the success of the Palmaz and Palmaz-Schatz stents marketed by Johnson & Johnson Interventional Systems, Warren, N.J. These stents are generally radially expandable cells and are well described in U.S. Pat. No. 4,733,655 to Palmaz incorporated herein by reference and the progeny of patents following the seminal Palmaz patent. Essentially, the stent comprises a material which is balloon expandable beyond its elastic limit. Generally these stents are formed from metal. This stent, when expanded beyond this elastic limit, maintains its position within the lumen of the body. The stent is able to hold open the lumen while maintaining its diameter beyond the elastic limit. This helps to enable passage of material through the lumen, most notably the flow of blood through the arteries, especially the coronary arteries.
It has been noted that in some instances one may desire to limit the amount of expansion of a balloon expandable stent. This may be (for instance) in situations where the lumen is of a known size and it is desired to have the stent be no more than the known size. While the manufacturer can certainly devise stents with the limitations of the known lumen in mind, in some instances it may be desirable to nevertheless limit the size of the stent so that the user can effectively choose a final diameter of the stent.
In addition, it has been found that it may be desirable to enhance circular or "hoop" strength while maintaining the stent beyond the elastic limit of the metal surface of the stent. This increased hoop strength may be useful in lumens where there are relatively high forces acting around the circumference of the stent. This may occur for instance in the arteries of the body.
With the foregoing in mind, the stent as described in this invention comprises a plurality of expandable cells. The cells are arranged circumferentially about the stent so that the stent in an unexpanded condition has a generally cylindrical construction and the expandable cells contain at least one metal bridge and at least one other circumferential arrangement of cells, and the bridge is initially arranged in a folded condition in the stent. When the cells expand, the bridge lengthens to a generally straight configuration. This straight configuration forms an arc of a circle about the cylindrical expandable stent. Ideally, there are multiple bridge connections made so that the stent has a full circumferential solid cross section along at least a portion of the cylindrical device.
The foregoing will be better understood in connection with drawings relating to the present invention.